The present disclosure relates generally to well drilling and completion operations and, more particularly, to in-situ borehole fluid speed and attenuation measurement in an ultrasonic scanning tool.
Well drilling and completion operations sometimes require the use of casings within a wellbore in a subterranean formation to ensure that the wellbore does not collapse once it is drilled and that sensitive areas of the formation are protected and isolated. In most cases the casings are secured in the wellbore using a cement layer that fills an annulus between and bonds to both the casing and the formation. The strength of both cement bonds is important to the integrity of the well. Measuring cement impedance can provide information about the strength of the cement bonds.
Some casing and cement evaluation tools transmit an acoustic pulse into the casing and cement layer, and receive an echo signal of that pulse. The echo signal may include reflections and reverberations caused by the casing, the cement layer, and an interface between the two. These reflections and reverberations may be used, in part, to calculate downhole characteristics, including the cement impedance. In some instances, borehole fluids, such as drilling mud and other formation fluids, may be present within the casing such that the acoustic pulse must be transmitted through the borehole fluid. The fluid speed and attenuation characteristics of the borehole fluid may alter or otherwise affect the initial acoustic pulse and the reflections and reverberations. Typical calculations to determine cement impedance, for instance, account for these affects, but the accuracy of the resulting determination depends, in part, on the accuracy of the fluid speed and attenuation values used in the calculations. In-situ measurements can be difficult for heavy mud, which can clog or otherwise cost sensors, and experimental estimations fail to account for the dynamic conditions downhole.
While embodiments of this disclosure have been depicted and described and are defined by reference to exemplary embodiments of the disclosure, such references do not imply a limitation on the disclosure, and no such limitation is to be inferred. The subject matter disclosed is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those skilled in the pertinent art and having the benefit of this disclosure. The depicted and described embodiments of this disclosure are examples only, and not exhaustive of the scope of the disclosure.